1. Field of the Invention
The present invention relates generally to methods for making polyurea and polyurea-urethane polymer compositions that can be used to make a variety of products, particularly golf balls. The methods involve preparing intermediate prepolymers that are reacted with chain extenders to form final polymer compositions. The invention also encompasses products, particularly golf balls, which can be made with such polymers.
2. Brief Review of the Related Art
Polyurethane and polyurea polymer compositions are used in a wide variety of products including fibers, sporting goods, toys, coatings, sealants and adhesives, films and linings, and flexible and rigid foams. Polyurethanes or polyureas, which may be either thermoplastic or thermosetting, are used to make the products depending upon end-use application. In recent years, there has been high interest in using polyurethanes and polyureas to make cover materials for golf balls.
Basically, polyurethane compositions contain urethane linkages formed by reacting an isocyanate group (—N═C═O) with a hydroxyl group (OH). Polyurethanes are produced by the reaction of a multi-functional isocyanate with a polyol in the presence of a catalyst and other additives. The chain length of the polyurethane prepolymer is extended by reacting it with a hydroxyl chain extender (curative). Polyurea compositions, which are distinct from the above-described polyurethanes, also can be formed. In general, polyurea compositions contain urea linkages formed by reacting an isocyanate group (—N═C═O) with an amine group (—NH or —NH2). The chain length of the polyurea prepolymer is extended by reacting the prepolymer with an amine chain extender (curative). Hybrid compositions containing urethane and urea linkages also may be produced. For example, a polyurea/urethane hybrid composition may be produced when a polyurea prepolymer is reacted with a hydroxyl-terminated curing agent.
In practice, two basic manufacturing techniques are used to form the polyurethane and polyurea compositions: a) one-shot technique, and b) prepolymer technique. For example, the one-shot technique, wherein the isocyanate and polyamine compounds and curing agent are reacted in one step, may be used to make polyureas. The isocyanate and polyamine compounds and curing agents along with additives, such as pigments, fillers, and/or light stabilizers, are mixed to form the final polyurea composition in a single reaction step. One example of a one-shot manufacturing process used for making polyurea or polyurethane materials such as flexible or rigid foams or plastic parts is known as reaction injection molding (RIM). In the RIM process, two highly reactive liquid streams are impinged and mixed together at high pressure and the reaction mixture is rapidly injected into a mold cavity. The two streams may be referred to as a polyurea or polyurethane system. The first stream containing the isocyanate compounds may be referred to as the “A” component and the second stream containing the polyamines and/or polyols and additives may be referred to as the “B” component.
The second technique, prepolymer manufacturing, involves multiple reaction steps. In a conventional prepolymer process, the isocyanate and polyamine compounds are mixed together at an excess stoichiometric ratio of isocyanate groups to amine groups, and the mixture is heated to produce an iscoyanate-terminated prepolymer. In turn, the prepolymer is reacted with an amine or hydroxyl-terminated curing agent (chain extender). In this reaction, the chain extender reacts with the residual NCO groups in the prepolymer to form the polyurea or polyurethane. Such conventional prepolymer manufacturing techniques are described in the patent literature.
For example, Turner et al., U.S. Pat. No. 4,686,242 discloses a process for preparing a polyurea or polyurea-urethane polymer that involves reacting an amine functional compound having an equivalent weight of at least about 400 with an excess of polyisocyanate to form an isocyanate-terminated prepolymer or quasi-prepolymer. In the next step, the isocyanate-terminated prepolymer or quasi-prepolymer is reacted with an isocyanate reactive material, preferably a low molecular weight polyamine or polyol, to form a polyurea and/or polyurea-urethane polymer that preferably has a non-cellular or microcellular structure.
Smith, U.S. Patent Application Publication 2002/107354 discloses a process for making a polyurea prepolymer, whereby a polyamine and caprolactone monomer are reacted to provide an open chain, linear aliphatic reaction product with a functional, terminal amine group at one end and a functional hydroxy group at the other end, The reaction product is reacted with aliphatic polyisocyanate, whereby the polyisocyanate reacts with each of the end groups to provide an aliphatic polyurea prepolymer.
Thiede, U.S. Patent Application Publication 2008/0097068 discloses a process for making an isocyanate-terminated prepolymer involving the steps of reacting a polycaprolactone polyol with a stoichiometric excess of an isocyanate mixture that contains at least 60 weight percent methylene diphenylisocyanate (MDI). The MDI comprises the 2,4′- and 4,4′-methylene diphenylisocyanate isomer in a molar ratio of from 25:75 to 80:20.
Today, the golf industry is developing cover layers for golf balls using castable, thermoset polyurethanes and polyureas. For example, multi-piece golf balls comprising a core, inner cover layer, and outer cover layer are used by many golf players today. The core is made commonly of a rubber material such as natural and synthetic rubbers, styrene butadiene, polybutadiene, poly(cis-isoprene), or poly(trans-isoprene). The inner cover layer may be made of a relatively hard material having a high flexural modulus such as ethylene-based ionomer resins. These ionomer acid copolymers contain inter-chain ionic bonding and are generally made of ethylene and a vinyl comonomer having an acid group such as methacrylic acid, acrylic acid, or maleic acid. Metal ions such as sodium, lithium, zinc, and/or magnesium are used to neutralize the acid groups in the copolymer. Ethylene-based ionomer resins are available in various grades and identified based on the type of base resin, molecular weight, type of metal ion, amount of acid, degree of neutralization, additives, and other properties.
The relatively hard inner cover provides the ball with good resiliency allowing the balls to reach a high speed when struck by a club. As a result, such golf balls tend to travel a greater distance, which is particularly important for driver shots off the tee and shots made with long irons. Meanwhile, the relative softness of the cover provides the player with a better “feel” when he/she strikes the ball with the club face. The player senses more control over the ball as the club face makes impact with the ball. Such softer covered balls tend to have better playability. The softer cover allows players to place a spin on the ball and better control its flight pattern. This is particularly important for approach shots near the green. Polyurethane and polyurea covered golf balls are described in the patent literature, for example, U.S. Pat. Nos. 5,334,673; 5,484,870; 6,476,176; 6,506,851; 6,867,279; 6,958,379; 6,960,630; 6,964,621; 7,041,769; 7,105,623; 7,131,915; and 7,186,777.
As discussed above, in the traditional prepolymer process, the isocyanate-terminated prepolymer is formed using a stoichiometric excess of isocyanate to polyols/polyamines so that all of the hydroxyl/amine groups will react with the isocyanate groups. One potential disadvantage with using conventional techniques to make an isocyanate-terminated prepolymer is that a high concentration of free isocyanate may be produced in the process. If a significant amount of residual isocyanate is generated, this may lead to potential environmental, health and safety issues.
Another potential disadvantage with conventional prepolymer manufacturing processes is that it may be difficult to use certain combinations of isocyanates, polyamines, and curing agents. Different isocyanate compounds may have significantly different reaction rates with polyamines and curing agents making it difficult to use isocyanate blends. Also, certain isocyanates may not be compatible with certain polyamines and curing agents. Furthermore, it can be difficult to handle and work with certain isocyanate compounds such as toluene diisocyanate (TDI), because of their relatively high vapor pressures and potential health and safety risks.
One objective of this invention is to develop a novel method for forming prepolymers so that manufacturers can use different combinations of isocyanate compounds, polyamines, and chain extenders in the formulations. Secondly, when polyurea compositions are used as cover materials for golf balls, the properties of the composition depend in significant part upon the components or building blocks used to make the compositions, particularly the isocyanates, polyamines, and curing agents. Prepolymers that can provide the final polyurea polymer compositions with desirable properties such as high tensile strength, flex modulus, impact durability, and cut/tear-resistance along with other advantageous properties would be of great benefit. One objective of this invention is to develop such prepolymers that can be used in turn to make polyurea polymer compositions having optimum properties. The present invention provides novel prepolymers having many advantageous properties, features, and benefits along with novel methods for making such prepolymers.